1. Field of the Invention
The present invention relates to an automatic focus position adjusting unit, and more particularly to an automatic focus position adjusting unit for use in a shadowless lighting device for medical purposes.
2. Description of the Related Art
A shadowless lighting device for medical purposes is utilized for illuminating a human body to be operated upon during an operation. This type of lighting device is capable of so illuminating a part to be operated upon that no shadows are formed. The lighting device is required to have an ability to adjust the focus position according to the desire of a surgeon. To adjust the focus position in such a way, an automatic focus position adjusting unit using supersonic waves has been known. This type of unit emits supersonic waves from the direction of illuminating lamps to the body to be operated upon, and detects the waves reflected from the body so as to measure the propagation distance based on the propagation time. The focus position is automatically adjusted based on the measured distance. An automatic focus position adjusting unit, using a transmitter which can be manipulated while being held in the surgeon's hand, is also known. In such a unit, the surgeon introduces the transmitter to a position at which he wants the focus position to be formed, and actuates the transmitter to send the signal. The signal transmitted from the transmitter is detected in the direction of the illuminating lamps, whereby the focus position is automatically adjusted so that it may move to the position where the transmitter has been introduced.
In the automatic focus position adjusting unit using supersonic waves, however, there is a problem in that when the illuminating lamps are positioned at an oblique angle with respect to the body to be operated upon, it is impossible to measure the distance correctly. That is, the part of the body which the surgeon wants the illuminating lamps to illuminate is the part of the body to be operated upon, so that the unit using supersonic waves does not permit an accurate measuring of the distance with respect to the part to be operated upon. Moreover, with the automatic focus position adjusting unit using the transmitter, a problem concerning the difficulty of handling the unit exists. In other words, the surgeon must introduce the transmitter into the vicinity of a part to be operated upon. During operations, such as a laparotomy, the part to be operated upon is located deep inside the body, and it is very difficult to introduce the transmitter so deep. In addition, a hygiene problem, such as secondary infection, may occur.